Process for halogenating molten metals



Aug. 27, 1968 p, A, RUBEL 3,399,029

PROCESS FOR HALOGENATING MOLTEN METALS Filed March 16, 1966 United States Patent 3,399,029 PROCESS FOR HALOGENATING MOLTEN METALS Peter A. Rubel, Lexington, Mass., assignor to Cabot Corporation, Boston, Mass., a corporation of Delaware `Filed Mar. 16, 1966, Ser. No. 534,716

8 Claims. (Cl. 23--93) This invention relates to the production of metal halides and more specifically to an improved process for the prO- duction of gaseous metal halides.

The reaction of halogen gases with molten metals to produce metal halides is a well known art and has attained aposition of significant industrial importance. In such a process, a halogen gas is generally -bubbled Ainto a chamber comprising a molten metal thereby producing the metal halide. This particular process has been generally foundpsuitable for producing chlorides and bromides of aluminum, tin, lead, zinc and the like.

However, many problems have heretofore been encountered in the production of metal halides. For instance, halogen gas is generally bubbled into the chamber of molten metal yby means of a tube or rod extending into the chamber to a point below the surface of said molten mass. Frequently, however, the tube or rod deteriorates from severe process conditions thereby providing an inadequate vehicle for the halogen gas. In addition, reaction of the halogen gas and molten metal often occurs at the exit end of the tube or rod causing plugging and contamination with metal halide at this point. Moreover, the reaction chamber is generally designed in such a manner that addition of metal to the chamber during chlorination is extremely diflicult, and accumulation of impurities which may build up within the chamber are diiiicult to remove. In accordance with the present invention, however, these problems have been substantially resolved.

It is a principal object of the present invention to provide an improved process for the production of metal halides.

It is another object of the present invention to provide improved apparatus for the production of metal halides.

It is still another object of the present invention to provide an improved process and apparatus for the production of aluminum chloride.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

Thefabove and other objects of this invention can be accomplished by (l) providing a packed and heated reaction chamber, (2) providing a reservoir of molten metal separate from, and circulating the molten metal through, the packed reaction chamber, and (3) introducing a halogen gas into the headspace at the top of the reaction chamber, thereby causing the halogen gas and molten metal to react largely within the reaction chamber proper.

The above and other objects and advantages of the present invention will be more readily understood when reference is had to the accompanying drawing forming part hereof wherein there is set forth a schematic, diagrammatic view of an apparatus of the :general type that can be utilized in the practice of the present invention, wherein a molten metal is circulated through a packed reaction chamber and a halogen gas introduced into the gaseous headspace of said chamber reacts with the molten metal largely within the area of the reaction chamber containing the packing to produce the metal halide.

In a typical operation referring now to the drawing, reservoir 1, lined'with frebrick or other suitable heat resistant material and containing metal and a metal flux, is heated to render the metal therein molten yby any suitable means such as by electrical means. Reaction chamber 3, also lined with rebrick or other suitable heat resistant 3,399,029 Patented Aug. 27, 1968 ICC material and packed with pieces or pebbles of a suitable packing material such as alumina, is also heated, for example, electrically. Molten metal from reservoir 1 is then circulated through packed reaction chamber 3 by means of pumps 9 and 11 and valves 5 and 7. Next, halogen gas is introduced into headspace 12 of reaction chamber 3 by means of inlet 13. Metal halide vapor is now generated within chamber 3 by reaction of halogen gas and molten metal and exits from chamber 3 through outlet 15 and is collected by any suitable means. It should be noted that pump 11 is so designed and operated that the molten metal and contaminants such as aluminum oxide flow back into the reservoir but the gaseous metal halide will not pass through the pump into the molten metal reservoir. The contaminants are picked up by the metal liux within the reservoir and dissolved.

It should be noted that the objects and advantages offered by the present invention over known prior art processes are achieved at least in part by utilization of a separate reservoir for the molten metal which reservoir also contains metal salts or uxes. The metal salts or uxes pick up and dissolve any contaminant coming in contact therewith and thereby the molten metal is generally free of contamination and the reservoir is easily maintained. In addition, despite the addition of halogen gas to headspace 12 of the reaction chamber, the generation of metal halide occurs largely within that area of the reaction chamber which contains the packing and not signilicantly at the input point of the gas. Moreover, the rate of production of metal halide can generally be controlled by the halogen Vgas input alone, and need not depend upon the rate of molten metal flow and/or temperature of the reaction chamber.

The metals that can be utilized for purposes of the present invention comprise in general, any metal that forms a volatile metal halide that can be readily removed from reaction chamber 3. For instance, the members of Groups IIb, IIIb and IV of the Mendeleev periodic system that form such volatile metal halides are entirely suitable. Definitely preferred, however, are metals such as aluminum, lead, tin and zinc.

The metal salts and fluxes utilized in practicing the present invention can vary to a large extent. However, the metal salts employed should generally be inert to the metal utilized, products of reaction, temperatures and pressures, etc. Fluxes that are suitable for purposes of the present invention are, in general, any substance that absorbs impurities from molten metals. Preferred, however, are fluxes which have a density somewhat lower than the metal utilized in molten form in order to prevent flux material from being pumped into the reaction chamber. Examples of fluxes that can be utilized in accordance with the present invention are various metal chlorides and bifluorides and mixtures thereof. More specific-ally, zinc chloride/ ammonium chloride complexes, sodium uoride/ aluminum fluoride complexes, barium chloride/ammonium chloride and the like can be employed in producing metal halides of this specification.

Halogen gases generally suitable for use in the practice of the present invention are bromine and chlorine. More preferred, however, for the purposes of this invention is chlorine. The halogen gas can be introduced into the reaction chamber alone or can be diluted with an inert gas such as nitrogen, if so desired. It should also be noted that the halogen gas generally need not be heated prior to entering into the reaction chamber, although heating of the halogen gas may be desired depending upon the particular metal utilized, the size of reaction chamber 3, flow r-ates, etc.

The size and design specifications of the molten metal reservoir forming part of this invention are normally flexible and many variations can be utilized. However,

it should be noted that determination of design specications such as shape and capacity, the materials utilized and the like are to some extent dependent upon the particular metal utilized, rate of metal halide production desired, extent of heating required, etc. Moreover, it is normally desirable to have a reservoir whose capacity is at least about twice the capacity of the reaction chamber.

The materials fromwhich the molten metal reservoir can be fabricated are subject to considerable variation. Generally any metal, metal alloy or ceramic composition which is substantially inert to the temperatures, reactants, and pressures to be utilized is suitable. For instance, materials that are generally suitable for the fabrications of the reservoir of the present invention are nickel, stainless steel, vitreous silica and the like. Moreover, it should be noted that the reservoir should be llined with heat resistant materials such as carbon, brick, iirebrick and the like.

The size and design specifications of the reaction charnber are likewise not critical. However, the design and specifications such as shape and capacity, packing material utilized and the like are somewhat dependent upon the reactants, products of reaction, temperatures, pressures, etc., utilized. Moreover, the materials from which the reaction chamber can be fabricated are generally subject to the same requirements described hereinbefore concerning the reservoir containing the molten metal.

The materials which can be utilized to pack the reaction chamber can vary to a large extent. However, said materials should be inert to the reactants, products of reaction, temperatures, pressures, etc., utilized in accordance with the present invention. Examples of packing materials suitable for purposes of this invention are alumina, silica, ceramic compositions and the like. A preferred embodiment of the present invention comprises the use of chips or pebbles of alumina as the packing material. The size of the chip or pebble of the material utilized is not critical. In general, chips or pebbles of about 1A .inch to l inch in diameter are entirely suitable.

The type of pumps utilized in the operation of the present invention can vary substantially. However, it should he noted that the type of pump utilized depends to a large extent upon, the temperatures, pressures, reactants, products of reaction, etc. For instance, magnetic flux pumps, centrifugal pumps, radial pumps and the like can be utilized. It should be further noted, however, that the pumps -are to be designed and operated so as to prevent metal halide product gases from entering the reservoir of molten metal. For instance, when magnetic flux pumps are employed, said pumps are wired in such a manner that electric current must flow through the stream being pumped when activated. The molten metal which -acts as a conductor is forced through the pump by the force exerted upon it by the electric current. However, metal halide gases which are not conductors of electricity are not allowed to pass through the pump.

A better understanding of the present invention can be obtained from the following example, which, however, should be construed as being illustrative in nature and not limiting the scope of the invention.

EXAMPLE To apparatus of the type illustrated in the drawing, comprising reservoir 1, having a 500 pound capacity for molten aluminum and fabricated from stainless steel lined with iirebrick is charged 400 pounds of aluminum metal and 40 pounds of sodium uoride/ aluminum uoride flux. The contents therein are heated to about 1500 F. by electrical heating means (not shown). Reaction chamber 3, also lined with tirebrick and packed with 200 pounds of one-half inch diameter alumina pebbles, is heated to about 1300 F. by electrical heating means (not shown). Next magnetic ux pumps 9 and 11 are activated and valves and 7 opened, thereby circulating molten aluminum metal from reservoir 1 through reaction chamber 3 by meansof conduits 17and 19 at a rate of about 13000 pounds per hour. Chlorine,- gas is then introduced into headspace 12 at a pressure of about 5 p.s.i.g. through inlet 13 and reaction of the chlorine and molten aluminum proceeds within chamber thereby producing aluminum chloride vapor. The aluminum chloride vapor exits from the bottom of reaction chamber 3 by means of conduit 15 and is collected by any suitable means. CoverfZ on top of reservoir 1 is opened every 6-8 hours andadditional aluminum metal is charged therein. After several days operation, most of the old ilux resident in the heated reservoir 1 is ladled out through cover 2 and a fresh supply of flux is supplied. After about 4 weeks of operation, the apparatus is shut down for examination. Reaction chamber 3 is found to be clean and in satisfactory condition.

Obviously, many changes can be made in the above example without departing from the scope of this invention. For instance, the apparatus of the present invention can be readily designed so as to utilize oxidizing agents other than chlorine. For example, phosgene and vcarbon tetrachloride can be utilized alone, or in combination with chlorine. Moreover, as mentioned hereinhefore,'bromine can be utilized in practicing the present invention.

What is claimed is:

1. A process for producing metal halides which comprises providing as separate entities a molten metal reservoir containing a molten metal which forms a volatile metal halide and is a member of the group consisting of Groups IIb, Illb or IV of the Mendeleev periodic system, and a packed reaction chamber having a headspace at the top thereof, circulating molten metal from said reservoir through said reaction chamber and back into said reservoir, and introducing a halogen gas which is a member of the group consisting of bromine and chlorine into said headspace thereby causing molten metal and halogen gas to react within said reaction chamber to produce the corresponding metal halide.

2. The process of claim 1 wherein there is present in said reservoir a iiux which removes impurities from the molten metal therein.

3. The process of claim 2 wherein' the flux utilized has a density lower than the molten metal.

4. The process of claim 2 wherein the ux utilized is a member of the group consisting of a zinc chloride/ ammonium chloride complex, sodium uoride/ aluminum fluoride complex or mixtures thereof.

5. The process of claim 1 wherein said molten metal is a member of the group consisting of aluminum, lead, tin or zinc.

6. The process of claim 1 wherein said molten metal is aluminum.

7. The process of claim 1 wherein said halogen gas is chlorine.

8. The process of claim 1 wherein the packing within said reaction chamber comprises `a member of the group consisting of alumina, silica, a ceramic composition or mixtures thereof.

References Cited UNITED STATES PATENTS 1,165,065 12/1915 Brooks 23-93 1,825,212 9/1931 Smith 23-98 1,937,419 1l/1933 Wolf et al 23-98 1,999,179 4/1935 Burgess 23-98 2,768,070 10/1956 Brazaitis 23--93 XR 3,052,518 9/1962 Frey 23-93 3,152,864 10/1964 Derham 23-93 3,236,608 2/1966 Cavadini et al.v 23-93 XR FOREIGN PATENTS 603,620 8/ 1960 Canada.

OSCAR R. VERTIZ, Primary Examiner.

EDWARD STERN, Assistant Examiner. 

1. A PROCESS FOR PRODUCING METAL HALIDES WHICH COMPRISES PROVIDING AS SEPARATE ENTITIES A MOLTEN RESERVOIR CONTAINING A MOLTEN METAL WHICH FORMS A VOLATILE METAL HALIDE AND IS A MEMBER OF THE GROUP CONSISTING OF GROUPS, IIB, IIIB OR IV OF THE MENDELEEV PERIODIC SYSTEM, AND A PACKED REACTION CHAMBER HAVING A HEADSPACE AT THE TOP THEREOF, CIRCULATING MOLTEN METAL FROM SAID RESERVOIR THROUGH SAID REACTION CHAMBER AND BACK INTO SAID RESERVOIR, AND INTRODUCING A HALOGEN GAS WHICH IS A MEMBER OF THE GROUP CONSISTING OF BROMINE AND CHLORINE INTO SAID HEADSPACE THEREBY CAUSING MOLTEN METAL AND HALOGEN GAS TO REACT WITHIN SAID REACTIN CHAMBER TO PRODUCE THE CORRESPONDING METAL HALIDE. 